1. Field of the Invention
The present invention relates in general to an image reader for reading information on an original to obtain the information in the form of electrical signals. In particular, the invention relates to an image reader for use in copying machines, scanners, and the like for which it is required to read information on an original at high speed.
2. Description of the Related Art
Heretofore, there is known a color image reader including light sources of equal to or larger than three colors, and an image sensor in which a plurality of image sensor ICs are mounted linearly, wherein in order to read image data at high speed, the image sensor ICs are divided into equal to or larger than two blocks to read out image signals of the blocks in the same period. This image sensor is described in JP 09-348339 A. This image sensor described therein will hereinbelow be described.
FIG. 11 shows a plan view of an example of a monochrome image sensor IC for use in a conventional color image reader.
Referring now to FIG. 11, image sensor ICs 1-1 to 1-9 having the same structure are mounted linearly on a substrate 107. Each of the image sensor ICs is provided with a start signal input terminal 103, a start signal output terminal 105, and an image signal output terminal 104, and these image sensor ICs are electrically connected to one another through a wiring pattern 112 distributed on the substrate 107 and bonding wires 106. Each of the image sensor ICs is provided with a light receiving element line 102. While not illustrated in FIG. 11, a clock pulse and a voltage from a power source are supplied to each of the image sensor ICs through the associated one of the bonding wires 106.
The image sensor ICs are divided into three blocks; a first block consisting of the image sensors ICs 1-1, 1-2 and 1-3, a second block consisting of the image sensor ICs 1-4, 1-5 and 1-6, and a third block consisting of the image sensor ICs 1-7, 1-8 and 1-9. The start signal input terminals 103 of the image sensor ICs, of the image sensor ICs of the blocks, which are mounted on the most left-hand side are all connected to a start signal input terminal 108 of the substrate 107. The start signal input terminals 103 of the image sensor ICs, in and after the second chips, of the image sensor ICs of the blocks are respectively connected to the start signal output terminals 105 of the image sensor ICs arranged therebefore by one.
In addition, the substrate 107 has three image signal output terminals, i.e., an image signal output terminal 109, an image signal output terminal 110, and an image signal output terminal 111. The image signal output terminal 109 is connected to the image signal output terminals 104 of the image sensor ICs 1-1, 1-2 and 1-3 through the associated ones of the bonding wires and the substrate wiring pattern. The image signal output terminal 110 is connected to the image signal output terminals 104 of the image sensor ICs 1-4, 1-5 and 1-6 through the associated ones of the bonding wires and the substrate wiring pattern. The image signal output terminal 111 is connected to the image signal output terminals 104 of the image sensor ICs 1-7, 1-8 and 1-9 through the associated ones of the bonding wires and the substrate wiring pattern.
As a result, the image signals of the image sensor ICs of the first, second and third blocks are respectively outputted through the image signal output terminals 109, 110 and 111. In addition, since a start pulse which has been inputted through a start pulse input terminal 108 of the substrate 107 is inputted to a start signal input terminal 3, being mounted on the most left-hand side, of the image sensor ICs of the blocks, the image signals of the blocks starts to be outputted simultaneously, and after completion of the output for three chips of the image sensor ICs, the output of the image signals of the blocks ends simultaneously.
FIG. 12 shows a timing chart useful in explaining an example of the operation of the conventional color image reader using the image sensor shown in FIG. 11.
Referring now to FIG. 12, when upon turning OFF a light source RED, a start pulse is inputted to the image sensor ICs 1-1, 1-4 and 1-7 through the start signal input terminal 108 of the substrate 7, image signals of a RED component start to be outputted from the corresponding light receiving elements of the image sensor ICs in the blocks. For the time required to output these image signals, there is only required the time required for the image sensor ICs of three chips to output the image signals of the RED component. A light source GREEN is turned ON after completion of the output from all of the image sensor ICs, and then all of the light receiving elements accumulate the carriers which have been generated due to the incidence of the reflected light, from an original, of the light emitted from the light source GREEN. When upon turning OFF the light source GREEN, the start pulse is inputted to the image sensor ICs 1-1, 1-4 and 1-7 through the start signal input terminal 108 of the substrate 107, image signals of the GREEN component start to be outputted from the corresponding light receiving elements of the image sensor ICs in the blocks. This is also applied to the BLUE component.
In such a conventional image reader, however, there is encountered the problem that the image is slipped between adjacent blocks as the original moves in the sub-scanning direction. For example, the last light receiving element of the first block is arranged adjacent to the first light receiving element of the second block, and hence a period of time required to accumulate the reflected light from an original differs depending on them. For this reason, the areas in which the adjacent light receiving elements read information on an original are slipped from each other in a sub scanning direction. Consequently, there is encountered the problem that the continuousness of an image is distorted in a joint between blocks in the reproduced image.
The foregoing problem is common to image readers that read image signals from image sensors arranged in a plurality of blocks simultaneously and is also common in image readers for reading monochrome images.